Thanks for all the replies. Even if my wife doesn't use it much, it could be a fun gift for her. (I have a tough time finding fun Christmas presents for her.) If I got one with a automatic shut off, we shouldn't need to worry about running down the battery too much.
I do have a small 400 watt inverter I could plug into the outlet I added to my trailer. I included a 15 amp fuse in my wiring, but the wiring I used was a bit thin as I only put it in to charge phones and tablets. Do you guys think a 120 volt AC blanket would draw too many amps? Would I need to replace the wiring on my DC plug to something thicker?
I'm thinking a blanket as she could wrap it around her as she's reading or lounging as much as for sleeping. She's a little more cold blooded than me and we've been avoiding using our furnace as it needs to be replaced.
(I have a Little Buddy Heater I use to taker the chill off before turning in or when waking up.)
Along with the typical 12 volt blankets, I've found there's a new one out there that's being marketed for backpacking that will run off a portable power pack or USB. Supposedly it run for 8 hours on low using a 10000 amp bank. I can't imagine it getting very warm, but the ability to pack it along when away from the RV is pretty neat. It's too new to have any reviews yet though...